Model calculations are presented which predict whether or not an arbitrary gas experiences significant absorption within carbon nanotubes and/or bundles of nanotubes. The potentials used in these calculations assume a conventional form, based on a sum of two-body interactions with individual carbon atoms; the latter employ energy and distance parameters which are derived from empirical combining rules. The results confirm intuitive expectation that small atoms and molecules are absorbed within both the interstitial channels and the tubes, while large atoms and molecules are absorbed almost exclusively within the tubes.Comment: 9 pages, 12 figures, submitted to PRB Newer version (8MAR2K). There was an error in the old one (23JAN2K). Please download thi

Using a finite-range density functional, we have investigated the energetics and structural features of mixed helium clusters. The possibility of doping the cluster with a molecule of sulfur hexafluoride is also considered. It is seen that the repulsion introduced by the impurity strongly modifies the properties of the smallest drops. Although only a qualitative comparison is possible, the gross features displayed by our calculations are in agreement with recent experimental findings. ͓S0163-1829͑97͒02438-7͔

An overview is presented of the various phases predicted to occur when gases are absorbed within a bundle of carbon nanotubes. The behavior may be characterized by an effective dimensionality, which depends on the species and the temperature. Small molecules are strongly attracted to the interstitial channels between tubes. There, they undergo transitions between ordered and disordered quasi-one dimensional (1D) phases. Both small and large molecules display 1D and/or 2D phase behavior when adsorbed within the nanotubes, depending on the species and thermodynamic conditions. Finally, molecules adsorbed on the external surface of the bundle exhibit 1D behavior (striped phases), which crosses over to 2D behavior (monolayer film) and eventually 3D behavior (thick film) as the coverage is increased. The various phases exhibit a wide variety of thermal and other properties that we discuss here.